Contouring or finishing articles formed of non-rigid materials such as silicone or organic rubbers, for example, has heretofore been quite difficult. Due to the nature of the materials, the article tends to flex, deform, or become distorted when engaged by the finishing tool. Furthermore, these characteristics are accentuated when the article is extremely thin as in the case of the contact lens. In the past, these articles have been frozen to impart enough rigidity to allow machining. The patent to Gomond, U.S. Pat. No. 3,750,272 which discloses freezing the soft contact lens using a spray of cooling fluid is an example of the freezing approach. Some of the problems of this approach is that certain materials require freezing temperatures which are difficult to achieve, the temperatures generated by the machining operates to bring the temperature of the article above its melting point and return it to its flexible state and finally in the frozen state such articles become very brittle leading to breakage. In the patent to Schpak et al., U.S. Pat. No. 3,423,886 the article, in this case a "soft" contact lens is secured to a mandrel and then rotated at high speeds so that centrifugal force imparts internal stresses in the edge which neutralize stresses induced by engagement with the forming element. The patent to Schrier, U.S. Pat. No. 3,736,183 discloses a method of centering lenses which increase the efficiency of the contouring or finishing provided by the centrifugal method.
Another method which has been proposed for machining an object formed of a non-rigid material is to sandwich the object between two pieces of a rigid material and machine the object while it is so held. In still another method which has been proposed, the object is encapsulated in a rigid medium, e.g., wax, and machined while it is encapsulated. Neither method, however, provides the accuracy which is desired in many applications, and hence, neither is acceptable for many applications. As disclosed by the reference patents, there are broadly speaking, three steps to manufacturing a molded soft contact lens. Namely, the molding steps, trimming and edging steps, and finally a finishing step. Part of this finishing step is to provide the lens with an edge portion which will not have any sharp portion which may cause pain to a patient wearing it while at the same time being thin enough to allow an efficient fit.